#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
	int n;
	double l;
	double a[1100];
	cin>>n>>l;
	for(int i = 0;i<n;i++)
	{
		cin>>a[i];
	}
	sort(a,a+n);
	double ans;
	for(int i = 0;i<n;i++)
	{
		if(i==0) ans = a[i];
		//else if(i==n-1) ans = max(ans,l-a[i]);
		else ans = max(ans,(a[i]-a[i-1])/2);
	}
	ans = max(ans,l-a[n-1]);
	printf("%.10lf",ans);
}
